Inbound authentication failed with error IllegalMessage for Receive connector Default MYEXSERVER.The authentication mechanism is ExchangeAuth. The source IP address of the client who tried to authenticate to Microsoft Exchange is [172.16.18.126].

The currently selected KDC certificate was once valid, but now is invalid and no suitable replacement was found. Smartcard logon may not function correctly if this problem is not remedied. Have the system administrator check on the state of the domain’s public key infrastructure. The chain status is in the error data.